This invention relates to a process for the preparation of secondary alkyl chlorides from alpha olefins. More particularly, this invention is directed to a method for the selective conversion of alpha olefins in the detergent range into 2-chloroalkanes by reaction with hydrogen chloride in the presence of a metal chloride catalyst supported on a porous carrier having a critically high average pore diameter.
Secondary alkyl chlorides are a well known class of organic compounds having a variety of utilities in commerce e.g. solvents, reaction intermediates, etc. It has long been known that secondary alkyl chlorides can be prepared from mono-olefins and hydrogen chloride by reacting the same in the presence of a metal chloride catalyst. For example, U.S. Pat. No. 2,103,692 discloses the hydrochlorination of the more reactive C.sub.2 to C.sub.6 olefins by vapor phase reaction with hydrogen chloride in the presence of certain di-and polyvalent metal chlorides e.g. ZnCl.sub.2 supported on carriers such as silica gel or activated silica acid. U.S. Pat. No. 2,705,734 extends this hydrochlorination reaction to the liquid phase through the employment of zinc chloride catalyst in the form of zinc chloride-hydrocarbon addition compounds or aqueous zinc chloride solutions.
A particularly useful class of secondary alkyl chlorides are the chloroalkanes derived from detergent range olefins i.e. monoolefins in the C.sub.7 to C.sub.30 range. Specifically, the 2-chloroalkanes derived from alpha olefins in this range may be used to prepare tertiary amines from which amine oxides, quanternary ammonium salts and zwitterionic detergents e.g. betaines and sulfobetaines may be prepared. In this regard, it would be desirable if this class of 2-chloroalkanes could be prepared by direct hydrochlorination of the detergent range alpha olefins in the presence of a supported metal halide catalyst because of the obvious advantages of the use of heterogeneous solid catalysts in large scale processes. However, one difficulty which is encountered in the hydrochlorination of detergent range alpha olefins using metal halide catalysts, e.g. ZnCl.sub.2 or ZnCl.sub.2, supported on ordinary carriers (e.g. ordinary silica which has an average pore diameter of usually below 20 m.mu.) is that isomerization of the olefins may take place resulting in the formation of an undesirable variety of secondary chlorides. For example, the hydrochlorination of alpha-olefins not only results in 2-chloroalkanes but also significant amounts of 3-and other internal chloroalkanes.
The present invention substantially overcomes the aforementioned deficiency in the catalytic hydrochlorination process of the prior art and, as a result, the invention provides an excellent means of obtaining 2-chloroalkanes in high selectivity from detergent range alpha olefins.